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[Display omitted] • Subduction-related geochemical signatures are observed in all silica compositions. • Hydrous melt signatures are strong along the magmatic belts farther from the suture. • Sediment melts signature is higher near the suture zone and decreases to the east. • Sediment melts suggest assimilated crustal components or relaminated sediments. • Assimilation of juvenile crustal components shows the stabilization of new crust. The closure of the Mongol-Okhotsk Ocean (MOO) marks the final suturing of the Central Asian Orogenic Belt, one of the largest accretionary orogens on Earth and a region that is considered an archetype for crustal growth during the Phanerozoic. Abundant Permian to Triassic magmatism in Mongolia extended into the Jurassic on the eastern side of the Mongol-Okhotsk Belt (MOB), the orogenic belt produced by the closure of the MOO. Magmatic belts formed north and south of the suture along the MOB provide insight into the dynamics of the subduction system and the magmatic, crustal, and mantle processes pre-, syn- and post- collision within this accretionary margin. One of the main questions regarding the magmatism in the region is: Was the magmatism formed during active subduction or during the collision and closure of the basin? Here we compile geochemical data (major and trace elements, and isotopes) from the Permian to Jurassic magmatic rocks in the MOB and analyze their spatiotemporal characteristics. Our goal is to assess how magmatism changed in time and space during the closure of the Mongol-Okhotsk Ocean and how those changes relate to first-order tectono-magmatic processes right before or during the collisional event that closed the basin. Our results show a general enrichment in fluid mobile elements, LILE, and LREE and depletion in HFSE, and HREE in mafic and felsic rocks, which indicates a mantle metasomatized by subduction-related fluids regardless of crustal contamination. Our analysis supports higher enrichment in sediment melts, especially along its western and older extent, and the assimilation of juvenile crustal components without producing abundant S-type peraluminous magmatism which indicates mantle and crustal contributions. Thus, we conclude that magmatism formed above a sediment-rich retreating margin was able to recycle and stabilize young and compositionally evolved crustal material in the Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

The Paleo-Mesoproterozoic Shillong Basin of the Assam-Meghalaya Gneissic Complex is exposed in parts of Northeast India. The studied metadolerites are from the volcano-sedimentary sequence of Shillong Basin from the Borjuri area in the Mikir Massif. This episode of mafic magmatism can be correlated with the Columbia supercontinent formation and bears significance to its reconstruction. The present work discusses the field, petrography and geochemical characteristics of the metadolerites, which occur in close association with the quartzites of the Shillong Group of rocks (metasedimentary rocks of the Shillong Basin). Our data show distinctive characteristics of subduction-related magmatism exhibiting high LREE/HREE, large ion lithophile element/high field strength element ratios and pronounced negative Nb anomaly. Elemental ratios such as Zr/Ba (0.21–0.46), La/Nb (1.23–2.32) and Ba/Nb (30.08–56.90) point to a fluid-enriched lithospheric mantle source in a subduction regime. Metadolerites plot in the field of 'back-arc basin basalts' in tectonic discrimination diagrams reinforcing a subduction zone tectonic setting. The mafic rocks correspond to a 6–10 % partial melting of a mantle source incorporating spinel+garnet lherzolite. The metamorphic P-T of the metadolerites estimated from plagioclase-hornblende geothermobarometer (7–8 kbar, 664 °C) is indicative of amphibolite facies metamorphism in a medium P-T zone. Based on the comparative analysis of field observation, petrography, geochemistry and geological ages given by previous workers, we infer that the Shillong Basin represents a back-arc rift region and is the eastern continuation of the Bathani volcano-sedimentary sequence of the Chotanagpur Granite Gneiss Complex marking continuation of the Central Indian Tectonic Zone to the Mikir Massif. [ABSTRACT FROM AUTHOR]

The Mogok Metamorphic Belt (MMB) of Myanmar formed during the Paleogene collision between the West Burma block and the Shan-Thai block. The MMB is mainly composed of medium to high-grade metamorphic marble, calc-silicate rocks, gneiss, quartzite, peridotite and igneous rocks such as granite, syenite and gabbro. The Mogok area in the central part of the MMB is well-known for magnificent quality ruby, spinel, sapphire, and peridot. To unravel the metamorphic PT-conditions prevailing during the formation of spinel and ruby from primary marble deposits in the Mogok area, three different types of high-grade quartz-garnet gneiss from the neighbourhood of gemstone mines were investigated by electron microprobe. Geothermobarometry reveals granulite facies PT-conditions of 756–792 °C at 7.4–7.6 kbar, which is reproduced by Theriak-Domino modelling within the error of both methods at water activities of 0.34–0.4. Shoshonitic and high-K calc-alkaline mafic dykes occur within marble forming conspicuous garnet-nepheline and clinopyroxene-clinoamphibole gneiss. Petrologic and geochemical investigations of these metadykes verify their granulite facies metamorphism and classify them as subduction-related magmatic rocks, which intruded the marble sequences. These investigations as well as previous studies show that spinel and ruby in marble of the Mogok area may have formed not only by metasomatism around alkaline intrusions, but also by granulite facies regional metamorphism.

Cadomian (Ediacaran–Cambrian) magmatic rocks have been reported in the eastern (e.g. the Çatalca and İhsaniye plutons) and western (e.g. the Binkılıç and Safaalan plutons) parts of the Istranca (Strandja) Massif. This paper aims to investigate the tectonic setting and the magma evolution history of the Cadomian magmatic rocks using both new and previously existing geochemical and geochronological data. The meta-granitoid rocks with intermediate to felsic composition are the main magmatic activity in the region. They intrude into metamorphic basement rocks composed of gneiss, schist, amphibolite, calc-schist, and quartzites (the Tekedere group). These plutons show strong foliation and traces of the polyphase metamorphism. All plutons are peraluminous and slightly metaluminous, mostly calc-alkaline and high-K calc-alkaline, and plot into the volcanic arc granites (VAG) field on the tectono-magmatic discrimination diagrams. The zircon U–Pb crystallization ages of the plutons are between 525.3 ± 3.5 Ma and 548.7 ± 2.3 Ma. Initial εNd values vary from −0.02 to 1.86. Nd-TDM model ages range between 1.08 and 1.24 Ga and indicate that the primitive magmas were originated and/or assimilated by the remelting of Neoproterozoic juvenile crustal rocks. New geochemical and geochronological data suggest a magma generation within a subduction-related magmatic arc setting in response to the southward subduction of the Proto-Tethys Ocean during the Late Precambrian-Early Palaeozoic period in the Istranca Massif. [ABSTRACT FROM AUTHOR]

Arc-related plutonic rocks in southern Mexico occur along the Pacific coast in the Sierra Madre del Sur (SMS) igneous province. These rocks record the migration of the Caribbean–North America–Farallon/Cocos junction towards the east between the Late Cretaceous and Miocene. However, little is known about the petrogenesis of igneous rocks that were emplaced during the latest expressions of magmatism in the SMS (i.e., early–middle Miocene). Based on fieldwork, petrography, whole-rock and mineral geochemistry, thermobarometric calculations, and zircon U Pb dating, we document the petrogenetic evolution of the Jalapa del Marqués pluton and adjoining intrusions, which are the youngest so far dated in the SMS and are located ∼150 km inland from the present-day trench. This subduction-related magmatic complex consists of granites, granodiorites, diorites, dacite porphyries, and intermediate-to-felsic dikes, whose geochemical features suggest early evolutionary processes driven by fractionation of amphibole ± clinopyroxene (moderate–high pressures) or plagioclase (low pressures). Pulses of evolved magmas were episodically injected into upper-crustal reservoirs (7–14 km) over ∼9 Myr, starting at 22.14 ± 0.65 Ma (2σ)—earlier than previously thought (∼15.7 Ma)—and producing subsequent pulses at 19.45 ± 0.36 Ma, from 16.36 ± 0.37 to 15.8 ± 0.34 Ma, and from 13.9 ± 0.5 to 13.3 ± 0.2 Ma. These ages correlate with the onset and early stages of volcanic centers in the Trans-Mexican Volcanic Belt (TMVB), some of which were located up to 500 km landward from the present-day trench. The large difference in the distance-to-trench between coeval magmatism in the Jalapa del Marqués pluton and the TMVB, indicates a variation in the subduction angle between two segments of the Farallon/Cocos Plate that were likely separated by a slab-tear. The eastward migration of this slab-tear (along with the triple junction) terminated the magmatic activity in the SMS by switching the locus of magmatism to the TMVB. This probably occurred shortly after the studied magmatic complex was assembled. • The Jalapa del Marqués pluton records the amalgamation of episodic magma pulses. • Magma injections from deep-crustal reservoirs consolidated upper-crustal mushes. • Subduction-related magmatism evolved in a normal-to-thickened crust. • The late Sierra Madre del Sur was coeval with the early Trans-Mexican Volcanic Belt. • Extinction of the Sierra Madre del Sur was caused by the migration of a slab-tear. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Two stages of Early-Middle Paleozoic magmatism are identified within the Ereendavaa terrane, Northeast Mongolia. • The 461–455 Ma Tsarig volcanic rocks formed in a continental arc setting as a result of northwestward subduction of the Paleo-Asian Ocean lithosphere. • The ~418 Ma Chandmana bimodal suite formed in a post-collisional extensional environment, probably related to the break-off of the Paleo-Asian Ocean slab. Abstract We report our newly obtained geochronological and geochemical data of volcanic rocks in the Tsarigiin gol area, Ereendavaa terrane to better understand of the Early-Middle Paleozoic tectonic evolution of the Kherlen massif, NE Mongolia. LA-ICP-MS zircon U-Pb dating reveals two stages of magmatism in the southern part of the Ereendavaa terrane: one in Late Ordovician (∼462 to 455 Ma) and the other in Early Devonian (∼418 Ma). The Late Ordovician Tsarig volcanic rocks are medium to high-K calc-alkaline and intermediate to felsic in composition and characterized by relative enrichment of LREE and LILEs (e.g., Rb and U) and also by relative depletion of HFSEs (e.g. Nb, Ta, P and Ti), a typical feature of subduction-related magmas. These rocks have mostly positive whole-rock Ɛ Nd (t) (+1.65 to +1.35) and zircon Ɛ Hf (t) (+0.1 to +4.07) values with Mesoproterozoic Nd and Hf model ages of 1.59–1.09 Ga. They were likely generated in a continental arc setting, and their parental magmas were originated from a common source as the product of extensive fractional crystallization of mafic melts and their interaction with arc crust. The Early Devonian Chandmana volcanic rocks consist of rhyolite and minor trachybasalt, displaying a typical bimodal distribution. The trachybasaltic rocks are characterized by low La n /Sm n (2.08–2.60), Tb n /Yb n (1.42–1.50) and La/Yb (7.51–8.96) ratios and relatively flat MREE to HREE patterns with Ɛ Nd (t) values being close to zero (−1.36 to +0.13). The rhyolites are high-K calc-alkaline and possess variably negative Ɛ Hf (t) (−4.96 to −0.29) and Ɛ Nd (t) (−2.14 to −0.57) values, exhibiting a strong affinity to A2-type granites. Considering the distinct compositional gap between the end-members and geochemical and isotopic signature of the bimodal suite, the felsic magma is interpreted to have derived from partial melting of a hybrid crustal source composed of both Pre-Neoproterozoic and juvenile crustal materials, while the mafic rocks were probably derived from a mantle source previously metasomatized by slab-derived melt. The two phases of magmatism in the southern part of the Ereendavaa terrane reflected two stages of tectonic evolution: Early-Middle Paleozoic subduction of the Paleo-Asian Ocean plate that gave rise to the Late Neoproterozoic-Early Cambrian Undur-Khaan island arc and Late Cambrian to Late Ordovician Ereendavaa active continental margin. Silurian amalgamation of the Ereendavaa and Idermeg terranes (Kherlen massif) caused the break-off of the subducted slab and the Early to Middle Devonian extension in the area. [ABSTRACT FROM AUTHOR]

We present geochronological, geochemical, and isotopic data on Statherian–Calymmian metaplutonites located within the Alto Moxotó Terrane (Borborema Province, Brazil). The Carnoió Suite occurs within a large area of this terrane. It is characterized by slightly deformed syenogranites and quartz-syenites, which present a geochemical signature typical of within-plate magmas. In contrast, the Coloete Suite occurs in the northern border area of the terrane. Its petrographic and geochemical characteristics vary between those of granodiorite and syenogranite, while its geochemistry suggests an arc-related/syn-collisional origin. There are few Statherian A-type granites in the Borborema Province and in its African counterpart. Zircon crystals recovered from the Carnoió Suite (dated 1638 Ma) and from the Coloete Suite (dated 1652 Ma; LA-ICP-MS) provide some clues about magma volume and concentration during the Statherian-Calymmian transition. Coeval collisional magmas are scarce in this region: they are interpreted worldwide as a product of peripheral convergences and coeval with the fragmentation of cratonic blocks. Our results suggest that the Alto Moxotó Terrane was part of an ancient block affected by an intraplate event during at the Statherian-Calymmian transition; moreover, its northern limits might have experienced accretion during a crust-reworking episode. • Statherian–Calymmian (∼1.6 Ga) crust evolution in central domain of the Borborema Province. • Continental fragmentation coeval with external orogen hypothesis. • Clues about magma volume as detrital zircon source. [ABSTRACT FROM AUTHOR]

The use of geodynamic information contained in sedimentary rocks has only recently been extended into the tectonic reconstruction studies of the Philippine archipelago vis-à-vis the rest of the Southeast Asian region. We present here a comparative assessment of clastic units from the western Central Philippines, particularly from the islands of Mindoro, Panay and Palawan, and propose their likely association with sources of Cathaysian origin. Geochronological data from sedimentary formations in the study areas register U–Pb dating peaks at 185–140 Ma, 140–120 Ma and 112–90 Ma. These are similar to those observed of detrital zircons from rocks of Cathaysian origin in Taiwan and Southern China that chronicle the Yanshanian magmatic events. These same formations also record an older intercept at 1.9–1.85 Ga that likely corresponds to a regional continental orogenic episode recorded in the late Paleoproterozoic Cathaysian block. Major (e.g. Al2O3/TiO2) and trace-element (e.g. Y/NivsCr/V) signatures of these sedimentary formations reflect stronger influences from granitic sources than mafic–ultramafic inputs that should otherwise be expected, considering their current oceanic island arc settings. Their La/Th and Th–Co–Zr/10 ratios also reveal continental island arc and active or passive continental margin depositional settings typical of rocks from the Palawan Microcontinental Block. New geochronological and geochemical data from the clastic rocks of northwest Mindoro, in addition to those already published for the other regions of the Palawan Microcontinental Block, provide further evidence for the amalgamation of fragments of Cathaysian origin within the Philippine island arc system. [ABSTRACT FROM AUTHOR]

Abstract: New maps of S velocity variation for the upper and middle crust making up the northwestern most corner of South America have been developed from cross correlation of ambient seismic noise at 52 broadband stations in the region. Over 1,300 empirical Green's functions, reconstructing the Rayleigh wave portion of the seismic wavefield, were obtained after time and frequency‐domain normalization of the ambient noise recordings and stacking of 48 months of normalized data. Interstation phase and group velocity curves were then measured in the 6–38 s period range and tomographically inverted to produce maps of phase and group velocity variation in a 0.5° × 0.5° grid. Velocity‐depth profiles were developed for each node after simultaneously inverting phase and group velocity curves and combined to produce 3‐D maps of S velocity variation for the region. The S velocity models reveal a ~7 km thick sedimentary cover in the Caribbean region, the Magdalena Valley, and the Cordillera Oriental, as well as crustal thicknesses in the Pacific and Caribbean region under ~35 km, consistent with previous studies. They also display zones of slow velocity at 25–35 km depth under regions of both active and inactive volcanism, suggesting the presence of melts that carry the signature of segmented subduction into the overriding plate. A low‐velocity zone in the same depth range is imaged under the Lower Magdalena Basin in the Caribbean region, which may represent either sublithospheric melts ponding at midcrustal levels after breaching through a fractured Caribbean flat slab or fluid migration through major faults within the Caribbean crust. [ABSTRACT FROM AUTHOR]

Walegen Au deposit is closely correlated with granitic intrusions of Triassic age, which are composed of granite and quartz porphyries. Both granite porphyry and quartz porphyry consist of quartz, feldspar and muscovite as primary minerals. Weakly peraluminous granite porphyry (A/ CNK=1.10-1.15) is enriched in LREE, depleted in HREE with Nb-Ta-Ti anomalies, and displays subduction-related geochemistry. Quartz porphyry is strongly peraluminous (A/CNK=1.64-2.81) with highly evolved components, characterized by lower TiO2, REE contents, Mg#, K/Rb, Nb/Ta, Zr/Hf ratios and higher Rb/Sr ratios than the granite porphyry. REE patterns of quartz porphyry exhibit lanthanide tetrad effect, resulting from mineral fractionation or participation of fluids with enriched F and Cl. LA-ICP-MS zircon U-Pb dating indicates quartz porphyry formed at 233±3 Ma. The ages of relict zircons from Triassic magmatic rocks match well with the detrital zircons from regional area. In addition, ∊Hf( t) values of Triassic magmatic zircons from the granite and quartz porphyries are -14.2 to -9.1 (with an exception of +4.1) and -10.8 to -8.6 respectively, indicating a crustal-dominant source. Regionally, numerous Middle Triassic granitoids were previously reported to be formed under the consumption of Paleotethyan Ocean. These facts indicate that the granitic porphyries from Walegen Au deposit may have been formed in the processes of the closing of Paleotethyan Ocean, which could correlate with the arc-related magmatism in the Kunlun orogen to the west and the Qinling orogen to the east. [ABSTRACT FROM AUTHOR]

In situ zircon Hf isotopic analysis was conducted to investigate the characteristics of source materials responsible for generations of the Phanerozoic granitoids in South Korea. The Hf isotopic data compiled from the literature together with this study revealed two principal types of source materials governing the generation of the Permo-Triassic granitoids. One type corresponds to long-lasting, ancient lithospheric materials having highly negative ε(t) values of -24.3 to -18.6 and is temporally equivalent to the Paleoproterozoic to Neoarchean basement rocks prevalent in South Korea. This type is a primary source material for the Triassic postorogenic granitoids in the Gyeonggi massif. The other type corresponds to juvenile materials accreted by Late Paleozoic continental arc magmatism. This relatively young crust occurs largely in and around the Gyeongsang basin. Systematic southeastward increase in ε(t) values of both Permo-Triassic and Jurassic granitoids indicates enhanced contributions of juvenile materials toward the paleo-trench. Such a trend is best explained by the chemical mixing of two principal types of source. Northern limit of chemical interactions between ancient and juvenile components is inferred to lie along the central Okcheon belt during the Permo-Triassic. However, this boundary has shifted southeastward in Jurassic to be defined by the Sunchang-Yecheon shear zone, a part of the Honam Shear Zone. The arc-related juvenile crust was also a principal source for the Cretaceous-Paleogene granitoids in the Gyeongsang basin. [ABSTRACT FROM AUTHOR]

Extensive exposure of intrusive igneous rocks along the Ross orogen of Antarctica—an ancient accretionary orogen on the margin of East Gondwana—provides an exceptional opportunity to study continental arc magmatism. There is significant petrologic and geochemical variability in igneous rocks within a ~ 500-km-long segment of the arc in southern Victoria Land. The conspicuous occurrence of carbonatite and alkaline silicate rocks (nepheline syenite, A-type granite, and alkaline mafic rocks) adjacent to large complexes of subalkaline granitoids is not adequately explained by traditional models for continental arc magmatism. Extensive geochemical analysis (> 100 samples) and zircon U–Pb geochronology ( n = 70) confirms that alkaline and carbonatitic magmatism was partially contemporaneous with the emplacement of large subduction-related igneous complexes in adjacent areas. Major pulses of subalkaline magmatism were compositionally distinct and occurred at different times along the arc. Large bodies of subalkaline orthogneiss and granite (sensu lato ) were emplaced over similar time intervals (ca. 25 Myr) to the north (ca. 515–492 Ma) and south (ca. 550–525 Ma) of the alkaline magmatic province, although the initiation of these major pulses of magmatism was offset by ca. 35 Myr. Alkaline and carbonatitic magmatism spanned at least ca. 550–509 Ma, overlapping with voluminous subalkaline magmatism in adjacent areas. The most primitive rocks from each area have similarly enriched trace element compositions, indicating some common characteristics of the magma sources along the arc. The samples from the older subalkaline complex have invariably low Sr/Y ratios (< 40), consistent with relatively shallow magma generation and differentiation. The younger subalkaline complex and subalkaline rocks within the area of the alkaline province extend to higher Sr/Y ratios (up to ~ 300), indicative of generation and differentiation at deeper levels. The significant spatial and temporal diversity in magmatism can be explained by a tectono-magmatic model that invokes alternating phases of extension and contraction in the overriding plate. The low Sr/Y magmatism of the earlier subalkaline complex and the largely contemporaneous alkaline and carbonatitic magmatism occurred during a phase of extension in the overriding plate ca. 550–525 Ma. The differences in composition of this early phase of magmatism can be explained by variable lithospheric thickness along the margin, with the alkaline magmas derived from partial melts of thick metasomatized lithosphere. The younger subalkaline complex was emplaced during a phase of contraction in the overlying plate ca. 515–505 Ma. The latest phase of (post-orogenic) magmatism occurred during extension in the overriding plate ca. 505–492 Ma. [ABSTRACT FROM AUTHOR]

The Baikal–Muya Foldbelt is one of the oldest and the most enigmatic terrain among the Central Asian Orogenic Belt. During the Early (1.0–0.8 Ga) and Late (0.8–0.6 Ga) Neoproterozoic orogenic cycles a notable amount of juvenile crust has been formed in subduction–collision settings along with the reworking of the existing Early Precambrian continental crust. The latter is perfectly presented within the North Muya metamorphic block (Anamakit–Muya zone) including the oldest high-pressure subduction-related rocks in the Central Asia. In order to evaluate the process of the juvenile crust formation in the Precambrian continental unit, whole-rock trace elements along with zircon U–Pb ages and Hf-isotopic composition were analyzed in granites of unknown age that intrude the Precambrian volcanic-sedimentary rocks of the Parama series in the southern North Muya Block. Combined geochemical and zircons isotopic studies indicate the formation of granites with the main pulse at ∼810 Ma due to partial melting of a juvenile mafic crust accompanied by reworking of the older crustal material from the continental arc basement. The composition of the granites was controlled by processes of intracrustal differentiation together with a probable contamination by older crustal substrate. Geochemistry and age of the studied granites are comparable to the granites of the Muya complex observed in the volcano–plutonic Kelyana–Irokinda zone. It is assumed that the Muya block and the Kelyana–Irokinda zone (terrane) had possibly been parts of the large continental-arc system beyond the Siberia margins. [ABSTRACT FROM AUTHOR]

Interactions between subduction dynamics and magma genesis have been intensely investigated, resulting in several conceptual models derived from geological, geochemical and geophysical data. To provide physico-chemical constraints on these conceptual models, self-consistent numerical simulations containing testable thermo-mechanical parameters are required, especially considering the three-dimensional (3D) natural complexity of subduction systems. Here, we use a 3D high-resolution petrological and thermo-mechanical numerical model to quantify the relative contribution of oceanic and continental subduction/collision, slab roll-back and tearing to magma genesis and transport processes. Our modeling results suggest that the space and time distribution and composition of magmas in the overriding plate is controlled by the 3D slab dynamics and related asthenospheric flow. Moreover, the decrease of the bulk lithospheric strength induced by mantle- and crust-derived magmas promotes the propagation of strike-slip and extensional fault zones through the overriding crust as response to slab roll-back and continental collision. Reduction of the lithosphere/asthenosphere rheological contrast by lithospheric weakening also favors the transmission of velocities from the flowing mantle to the crust. Similarities between our modeling results and the late Cenozoic tectonic and magmatic evolution across the eastern Mediterranean region suggest an efficient control of mantle flow on the magmatic activity in this region, which in turn promotes lithospheric deformation by mantle drag via melt-induced weakening effects. [ABSTRACT FROM AUTHOR]

The relationship between subduction dynamics and crustal deformation in the Mediterranean region has been recently studied using three-dimensional (3D) models. Such models require, however, detailed information concerning the past geological evolution. We use stratigraphic, petrologic, metamorphic, structural, paleomagnetic and magmatic data to build new kinematic reconstructions of the eastern Mediterranean region since the late Cretaceous using the principle of non-rigid domains. The motions of the 56 deforming domains defined in this work are calculated based on published paleomagnetic rotations, the directions and amounts of displacement on crustal-scale shear zones and the burial and exhumation histories of the main metamorphic units. Extracted from these reconstructions, paleotectonic maps and lithospheric-scale cross-sections illustrate that the present-day subduction zone has been continuously retreating southward since the late Cretaceous and has accreted several small continental domains in the process. We find evidence for two back-arc-related extensional events: (1) slow extension along the Balkans and the Pontides in the late Cretaceous while the trench was long and linear and (2) faster extension in the Rhodope-Aegean-west Anatolian region since the Eocene–Oligocene. Rapid rotation of the Hellenides between 15 and 8 Ma probably indicates a slab tearing event below western Anatolia that could have further accelerated this extensional kinematics. Spatial distribution and the geochemical signature of magmatic centers integrated in these reconstructions allow us to trace mantle-related processes revealing the deep dynamics that controls both the magma genesis and the crustal deformation. [ABSTRACT FROM AUTHOR]

This study focuses on the Elbeyli–Ordu, Emeksen–Giresun, Güzelyayla–Trabzon and Ulutaş–Ispir porphyry-type prospects located in the Eastern Pontides, Turkey. Our new LA-ICP-MS U–Pb zircon age data reveal that the Elbeyli–Ordu Mo–Cu mineralization is hosted by a 77.0 ± 1.3 Ma-old monzonite/monzodiorite with a shoshonitic character. The Emeksen Mo mineralization, located ~ 40 km southeast of the Elbeyli–Ordu prospect, consists of NW- and NE-striking quartz veins crosscutting a high-K calc-alkaline to shoshonitic granite dated at 78.5 ± 0.8 Ma, a granodiorite dated at 78.7 ± 0.5 Ma and porphyry granite dated at 77.7 ± 0.5 Ma. The Güzelyayla porphyry Cu–Mo prospect consists of a stockwork-type Cu–Mo mineralization crosscutting a calc-alkaline 81.4 ± 1.1 Ma-old dacite porphyry and Late Cretaceous calc-alkaline andesite. The Ispir–Ulutaş mineralization is hosted within a highly sericitized 131.1 ± 0.9 Ma-old quartz-porphyry that intruded into a 132.9 ± 0.6 Ma-old calc-alkaline granite porphyry. Our new U–Pb zircon ages, lithogeochemical and radiogenic isotopic data of the host rocks associated with the porphyry-type prospects in the Eastern Pontides indicate that they formed in an arc-related environment during Cretaceous subduction of the Neotethys Ocean, and the Ispir–Ulutaş prospect is attributed to the main stage of the northward subduction of the Neotethys during the Early Cretaceous. We conclude that the Güzelyayla and Emeksen hydrothermal systems were formed during a transitional compressional to extensional tectonic evolution, whereas the Late Cretaceous Elbeyli hydrothermal system was emplaced during an extensional arc magmatic event. Highly-oxidized, high-K calc-alkaline to shoshonitic magmas at Emeksen and Elbeyli were derived from a metasomatized, heterogeneous and enriched lithospheric mantle, with variable degrees of partial melting of the mantle wedge and variable crustal contamination. Mixing/mingling processes between mafic magmas derived from the lower crust and acidic magmas at upper crustal levels played an important role in the formation of Cu–Mo porphyry-type mineralization in the Eastern Pontides. [ABSTRACT FROM AUTHOR]

Isla El Tigre volcano is located in the Gulf of Fonseca (Honduras) along the Central America volcanic front, where a significant change in the strike of the volcanic chain is observed. The studied samples of this poorly investigated volcano are mainly subalkaline basic to intermediate lavas (basalts and basaltic andesites) and subordinate subalkaline/alkaline transitional basalts, both having the typical mineralogical and geochemical characteristics of arc volcanic rocks. On the basis of petrographic and geochemical features, two groups of rocks have been distinguished. Lavas from the main volcanic edifice are highly porphyritic and hy–qz normative, and have lower MgO contents (< 5 wt.%). They show significant LILE and LREE enrichments and Nb–Ta depletions, and have a strong slab signature as well as incompatible element contents similar to those of the main front of the adjacent volcanoes in El Salvador and Nicaragua (e.g., Ba/La up to 80). In contrast, lavas from the parasitic cones have higher MgO contents (> 5 wt.%), are ol–hy normative and show lower HFSE depletions relative to LILE and LREE, with lower Ba/La, Ba/Nb and Zr/Nb ratios. This suggests that mantle-derived magmas were not produced by the same process throughout the activity of the volcano. The bulk rock geochemistry and 87 Sr/ 86 Sr (0.70373–0.70382), 143 Nd/ 144 Nd (0.51298–0.51301), 206 Pb/ 204 Pb (18.55–18.58), 207 Pb/ 204 Pb (15.54–15.56) and 208 Pb/ 204 Pb (38.23–38.26) isotopic data of Isla El Tigre compared with the other volcanoes of the Gulf of Fonseca and all available literature data for Central America suggests that this stratovolcano was mainly built by mantle-derived melts driven by slab-derived fluid–flux melting, while magmas erupted through its parasitic cones have a clear signature of decompression melting with minor slab contribution. The coexistence of these two different mantle melting generation processes is likely related to the complex geodynamic setting of the Gulf of Fonseca, where the volcanic front changes direction by ca. 30° and two fundamental tectonic structures of the Chortis continental block, mainly the N–S Honduras Depression and the NE–SW Guayape Fault Zone, cross each other. [ABSTRACT FROM AUTHOR]

The Maçka subvolcanic intrusions (MSIs) in the eastern part of the Sakarya zone, northeastern Turkey, play a critical role in understanding the petrogenetic and geodynamic processes that took place during the growth of Late Cretaceous arc crust of this region. U–Pb zircon (79.97 ± 0.97 Ma) and two40Ar–39Ar amphibole ages (average 81.37 ± 0.5 Ma) indicate that the MSIs were emplaced in Late Cretaceous (Campanian) time into the coeval volcanic rocks. A slightly younger zircon fission track (FT) age (73 ± 9 Ma) points to a rapid exhumation and cooling after crystallization. The intrusions are observed in areas less than 1 km2in the field and contain abundant mafic microgranular enclaves (MMEs). The host rocks (HRs) are entirely composed of tonalite (SiO2 = 63–65 wt.%, Mg# = 43–52), and the MMEs are gabbro-diorite in composition (SiO2 = 53–57 wt.%, Mg# = 45–48). Both the HRs and the MMEs are I-type, high-K calc-alkaline in composition and display a metaluminous character. They are characterized by geochemical features typical for magmas of subduction-related environments. Chondrite-normalized REE patterns are moderately fractionated [(La/Yb)N = 6–11] and display slightly negative Eu anomalies (Eu/Eu* = 0.7–0.9), with weak concave-upward REE patterns, suggesting that amphibole fractionation played a role during their evolution. The MMEs have slightly differentISr(0.7081–0.7085) and εNd(−5.0 to −5.4) values compared with those of their HRs (ISr = 0.7084–0.7087 and εNd = −5.7 to −6.9), indicating that variable amounts of crustal and mantle components were involved in the generation of parental magma to these rocks. All of these data, combined with those of previous regional studies, suggest that the MSIs are hybrid in origin, produced by the mixing of enriched lithospheric mantle- and lower crust-derived melts in an extensional arc setting that was caused by slab rollback. [ABSTRACT FROM AUTHOR]

The Yili Block is located at the Chinese western Tianshan and is a constituent of the Kazakhstan microcontinent. It played an important role in the evolution of the SW Central Asian Orogenic Belt (CAOB). The Yili Block underwent the Paleozoic orogeny during the subduction and closure of the Junggar Ocean. Late Paleozoic arc-type magmatic rocks have been widely recorded in the Yili Block; however, it remains poorly constrained when and how the Junggar Ocean started to subduct beneath the Yili Block. In this study, we report new results of zircon LA-ICP-MS U Pb dating and Lu Hf isotopic analysis on a series of bentonite beds in tightly folded upper Ordovician siliceous black shales of the Guozigou Section in the northern Yili Block. The occurrence of bentonite layers and associated sulfides within graptolite-bearing siliceous black shales indicates multiple marine volcanic eruptions. Magmatic zircons separated from seven representative bentonite samples yielded consistent U Pb ages ranging from 449.5 ± 2.4 Ma to 444.8 ± 2.0 Ma (Katian). In situ zircon Lu Hf isotopic analyses show mostly positive εHf(t) values (−0.01 and 1.31 to 11.7) and Neoproterozoic single-stage Hf model ages (T DM1 = 0.6– 1.0 Ga). A linear correlation between the εHf(t) and T DM1 suggests that these zircons likely crystallized from a common magma originated from a depleted mantle source with variable involvement of Precambrian continental crust. Our new zircon ages and Hf isotopic data are comparable with those of the Middle-Late Ordovician continental arc-type magmatic rocks in the nearby Wenquan area, both indicating that the subduction of the Junggar Ocean beneath the northern Yili Block started in the Middle-Late Ordovician, and are therefore important for early Paleozoic paleogeographic and tectonic reconstruction of the Paleo-Asian Ocean domain. In addition, the Late Ordovician marine bentonites and black shales coincide with the worldwide intensive volcanic activities and related climate/environment changes during late Katian to Hirnantian. Thus, these new data also provide further arguments for possible causes of the global climate change and mass extinction during the Ordovician-Silurian transition. [Display omitted] • Precise constraints on the deposition age of Ordovician marine sequence in northern Yili Block • Record for Mid-Late Ordovician initial subduction of Junggar Ocean beneath the Yili Block • Arguments for worldwide Ordovician-Silurian transition volcanism and major global events [ABSTRACT FROM AUTHOR]

Abstract: The Longwood Igneous Complex (LIC) is located in Southland, New Zealand on the eastern side of the Carboniferous to Cretaceous, I-type, Median Batholith. Intrusives of the Complex range in age from Permian to Jurassic and show trace element characteristics typical of subduction-related magmas. Gabbro, gabbroic diorite and basaltic dyke rocks show trace and minor element patterns and isotopic compositions indicating that they represent magmas generated in an intra-oceanic subduction system. Radiometric ages decrease across the LIC from 254Ma in the east to 142Ma in the west and mineral chemistry and mineral phase relationships indicate emplacement at depths between 15 and 25km. Thus the petrology and geochemistry of the LIC provides the basis for evaluating the composition of lower–middle crust assembled above a long lived intra-oceanic subduction system and we estimate this to be andesitic and similar to bulk continental crust. Rocks of the LIC range in composition from troctolite and gabbro through diorite to trondhjemite and granite. All of the ultramafic rocks and most of the gabbros have petrographic and geochemical features consistent with a cumulate origin and mineral chemistry shows similarities with arc cumulate sequences from elsewhere. Few of the plutonic rocks making up the LIC have direct analogues among modern intra-oceanic volcanic rocks. The latter are the end products and the former the leftovers from magmatic processes that included fractional crystallisation, crustal assimilation and magma mixing and mingling. Longwood intrusions do not represent magma chambers. They formed as crystal cumulates and mushes left over from the processes that generated magmas erupted at the contemporary volcanic arc. A correlation between decreasing age of emplacement and Sr and Nd isotopic compositions and inheritance in zircons dated by ion probe are indications of crustal recycling. The generation of felsic rocks in the Longwood intra-oceanic arc involved crustal anatexis and, over the 100million year history of the arc, the crust evolved towards a composition similar to bulk continental crust and average andesite. Dioritic rocks of the LIC contain abundant mafic enclaves, which are argued to represent fragments of mafic magma, derived by fractional crystallisation from basalt, which was intruded into a hot but solid or near solid diorite. Heating and remobilisation of the dioritic host disrupted and disaggregated the intruding mafic magma to form enclaves and zones of intrusion breccia that show every variation from liquid–liquid to liquid–solid mingling and mixing. They were then further modified chemically and mineralogically by diffusion of H2O, Na, P, Ba, REE, and, to a lesser extent, Rb. Mafic dykes occur throughout the Complex and a number of these are composite with compositions ranging from dolerite through andesite to dacite. The components of composite dykes do not define unequivocal linear mixing trends and hybridisation processes that took place within them have only localised significance; mingling and hybridisation in the composite dykes do not appear to have controlled geochemical variation among the major intrusive units of the Complex. [Copyright &y& Elsevier]

Abstract: Late Paleozoic magmatic rocks (including basic dykes, basaltic andesite, rhyolite, keratophyre and syenite-porphyry with minor tuff) are widespread in the western margin of the East Junggar terrane. In-situ zircon U–Pb dating and Hf isotope analyses were carried out for these magmatic rocks from the Baijiangou and Zhangpenggou localities of East Junggar, integrating with geochemical data, to investigate their tectonic evolution as well as crustal accretionary process of this region in the Late Paleozoic. Inherited zircons from basic dykes range in age from 435Ma to 300Ma. The Zhangpenggou rhyolite and keratophyre have typical arc-like geochemical signatures and were formed in the Early Carboniferous (332Ma and 336Ma, respectively), suggesting they are products of subduction-related magmatism. The Baijiangou rhyolites were formed in the Late Carboniferous (315Ma and 323Ma) and their formation ages are similar to those of the syenite-porphyries (307Ma and 312Ma). The Hf model ages and the formation ages of zircons from these magmatic rocks are alike, with positive εHf(t) values vary from +0.7 to +16.6, implying that voluminous growth of juvenile crust happened in the East Junggar terrane during the Late Paleozoic. The absence of Precambrian inherited zircons in basic dykes indicates the lack of Precambrian basement beneath the East Junggar terrane. Taking geochronological studies on regional ophiolites into account, the East Junggar terrane is considered as a Devonian–Carboniferous oceanic island arc which has been continuously accreted to the southern active margin of the Siberian Craton since the Early Carboniferous. [Copyright &y& Elsevier]

Abstract: The central-western Mediterranean area is a key region for understanding the complex interaction between igneous activity and tectonics. In this review, the specific geochemical character of several ‘subduction-related’ Cenozoic igneous provinces are described with a view to identifying the processes responsible for the modifications of their sources. Different petrogenetic models are reviewed in the light of competing geological and geodynamic scenarios proposed in the literature. Plutonic rocks occur almost exclusively in the Eocene–Oligocene Periadriatic Province of the Alps while relatively minor plutonic bodies (mostly Miocene in age) crop out in N Morocco, S Spain and N Algeria. Igneous activity is otherwise confined to lava flows and dykes accompanied by relatively greater volumes of pyroclastic (often ignimbritic) products. Overall, the igneous activity spanned a wide temporal range, from middle Eocene (such as the Periadriatic Province) to the present (as in the Neapolitan of southern Italy). The magmatic products are mostly SiO2-oversaturated, showing calcalkaline to high-K calcalcaline affinity, except in some areas (as in peninsular Italy) where potassic to ultrapotassic compositions prevail. The ultrapotassic magmas (which include leucitites to leucite-phonolites) are dominantly SiO2-undersaturated, although rare, SiO2-saturated (i.e., leucite-free lamproites) appear over much of this region, examples being in the Betics (southeast Spain), the northwest Alps, northeast Corsica (France), Tuscany (northwest Italy), southeast Tyrrhenian Sea (Cornacya Seamount) and possibly in the Tell region (northeast Algeria). Excepted for the Alpine case, subduction-related igneous activity is strictly linked to the formation of the Mediterranean Sea. This Sea, at least in its central and western sectors, is made up of several young (<30Ma) V-shaped back-arc basins plus several dispersed continental fragments, originally in crustal continuity with the European plate (Sardinia, Corsica, Balearic Islands, Kabylies, Calabria, Peloritani Mountains). The bulk of igneous activity in the central-western Mediterranean is believed to have tapped mantle ‘wedge’ regions, metasomatized by pressure-related dehydration of the subducting slabs. The presence of subduction-related igneous rocks with a wide range of chemical composition has been related to the interplay of several factors among which the pre-metasomatic composition of the mantle wedges (i.e., fertile vs. refractory mineralogy), the composition of the subducting plate (i.e., the type and amount of sediment cover and the alteration state of the crust), the variable thermo-baric conditions of magma formation, coupled with variable molar concentrations of CO2 and H2O in the fluid phase released by the subducting plates are the most important. Compared to classic collisional settings (e.g., Himalayas), the central-western Mediterranean area shows a range of unusual geological and magmatological features. These include: a) the rapid formation of extensional basins in an overall compressional setting related to Africa-Europe convergence; b) centrifugal wave of both compressive and extensional tectonics starting from a ‘pivotal’ region around the Gulf of Lyon; c) the development of concomitant Cenozoic subduction zones with different subduction and tectonic transport directions; d) subduction ‘inversion’ events (e.g., currently along the Maghrebian coast and in northern Sicily, previously at the southern paleo-European margin); e) a repeated temporal pattern whereby subduction-related magmatic activity gives way to magmas of intraplate geochemical type; f) the late-stage appearance of magmas with collision-related ‘exotic’ (potassic to ultrapotassic) compositions, generally absent from simple subduction settings; g) the relative scarcity of typical calcalkaline magmas along the Italian peninsula; h) the absence of igneous activity where it might well be expected (e.g., above the hanging-wall of the Late Cretaceous–Eocene Adria–Europe subduction system in the Alps); i) voluminous production of subduction-related magmas coeval with extensional tectonic régimes (e.g., during Oligo-Miocene Sardinian Trough formation). To summarize, these salient central-western Mediterranean features, characterizing a late-stage of the classic ‘Wilson Cycle’ offer a ‘template’ for interpreting magmatic compositions in analogous settings elsewhere. [Copyright &y& Elsevier]

Abstract: The andesitic volcano Ngauruhoe, which is located within the Tongariro Volcanic Complex at the southern end of the Taupo Volcanic Zone in North Island, New Zealand, has been constructed over the past 5ka and last erupted in 1975. Nearby Ruapehu volcano has a much longer eruptive history extending back beyond 230kaB.P. The magmas erupted at both volcanoes have been predominantly medium-K basaltic andesites and andesites, which evolved through polybaric crystal fractionation and assimilation processes that took place within complex, dispersed magmatic storage systems. Despite their close spatial proximity, the two volcanoes show geochemical contrasts suggesting that in each case both the mantle-derived parental magmas and the crustal assimilants were different. Variations in major and trace element data for Ngauruhoe lavas indicate control by crystal fractionation and assimilation (AFC) but the data are difficult to reconcile with derivation from a single batch of compositionally unique, mantle-derived parental basalt. Geochemical variation can be approximated by generalised AFC models using average basement or crustal xenolith compositions but precise mathematical modelling is limited because of the sensitivity of models to the selection of a particular parental composition and the difficulty of determining the exact nature of the crustal assimilant compositions that might have been involved in each specific case. U–Th isotopic data for Ngauruhoe volcanic rocks show disequilibrium that defines a positively inclined array lying to the right of the equiline on a 230Th/232Th versus 238U/232Th diagram. U-series data for Ngauruhoe and post 1945AD Ruapehu eruptives show similar patterns of disequilibrium but the Ngauruhoe data define an array with a different slope and a different intercept on the equiline. 230Th/238U ratios in Ngauruhoe lavas range from close to secular equilibrium (0.979) to 0.864 with the youngest (post 1870AD) eruptives showing the least disequilibrium. 230Th/238U and 87Sr/86Sr ratios are correlated; the samples with the highest 87Sr/86Sr values show the least disequilibrium. There is also a correlation between eruption age and Nd and Pb isotopic composition; the oldest samples tend to show the least radiogenic isotopic ratios. These data, in combination with major and trace element abundance data indicate that Ngauruhoe U–Th disequilibrium is determined by variations in parental magmatic compositions and AFC. Unlike the mature, long-lived Ruapehu system, Ngauruhoe''s eruptive cycles can be directly connected to periodic magma recharge from the lower crust and mantle. For Ngauruhoe eruptives, 226Ra/230Th varies from 1.218 to 1.492. This compares with a range of 0.972 to 1.186 for Ruapehu lavas erupted between 1945 and 1996. Reconciling the 226Ra/230Th data with decay during fractional crystallisation requires relatively low rates of fractionation (1–5×10−5/year) and short (1000–2000years) fractionation times. [Copyright &y& Elsevier]

Abstract: The Quaternary Acatlán Volcanic Field (AVF) is located at the western edge of the Trans-Mexican Volcanic Belt (TMVB). This region is related to the subduction of the Pacific Cocos and Rivera plates beneath the North American plate since the late Miocene. AVF rocks are products of Pleistocene volcanic activity and include lava flows, domes, erupted basaltic andesite, trachyandesite, trachydacite, and rhyolite of calc–alkaline affinity. Most rocks show depletion in high field-strength elements and enrichment in large ion lithophile elements and light rare earth elements as is typical for magmas in subduction-related volcanic arcs. 87Sr/86Sr values range from 0.70361 to 0.70412, while ɛNd values vary from +2.3 to +5.2. Sr–Nd isotopic data plot along the mantle array. On the other hand, lead isotope compositions (206Pb/204Pb=18.62–18.75, 207Pb/204Pb=15.57–15.64, and 208Pb/204Pb=38.37–38.67) give evidence for combined influences of the upper mantle, fluxes derived from subducted sediments, and the upper continental crust involved in magma genesis at AVF. Additionally δ18O whole rock analyses range from +6.35‰ in black pumice to +10.9‰ in white pumice of the Acatlán Ignimbrite. A fairly good correlation is displayed between Sr as well as O isotopes and SiO2 emphasizing the effects of crustal contamination. Compositional and isotopic data suggest that the different AVF series derived from distinct parental magmas, which were generated by partial melting of a heterogeneous mantle source. [Copyright &y& Elsevier]

• There are 757 Ma high-Ti tholeiitic basalts in the western Jiangnan orogen, Hunan Province. • The 757 Ma magmas formed in an intracontinental rift rather than a mantle plume. • Divergent double-sided subduction followed by collision formed the Jiangnan orogen. • Observations support placement of the South China Block along the margin of Rodinia. Widely distributed Meso- to Neoproterozoic igneous rocks record the evolution of the Jiangnan orogen. We present integrated geochemical and geochronological data for basalts from the Gaoqiao area, northwestern Hunan Province. U-Pb dating of zircons indicates that the formation of Gaoqiao basalts occurred in the Neoproterozoic, no earlier than 757 ± 16 Ma. Like the contemporaneous mafic rocks in neighboring areas, the Gaoqiao basalts show trace element characteristics suggesting derivation from a source similar to ocean-island basalts (OIBs), including strong enrichment in large-ion lithophile elements (LILEs), high-field strength elements (HFSEs) and TiO 2 , and high Ti/Y ratios. Placed in a regional tectonic context, however, the Gaoqiao suite is most consistent with an intracontinental rift model and offers no support to the idea of ongoing subduction in middle-late Mid-Neoproterozoic time in the western Jiangnan orogen. Despite the coincidence between the age of this rift and the separation of East Antarctica-Australia from Laurentia, we argue that the rift recorded in the South China Block (SCB) was an independent and probably unrelated event during the break-up of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]